My long range goal is to understand the mechanism of cytokinesis. We will pursue complementary cellular, biochemical and genetic strategies using the fission yeast Schizosaccharomyces pombe to address the following specific aims: Project 1. Dynamics of contractile ring proteins: these quantitative experiments on molecules in live cells-will provide the parameter values required to decipher the pathway of contractile ring assembly. We will measure the rates that cytokinesis proteins exchange between the cytoplasm and contractile rings, determine if actin filaments influence the dynamics of each contractile ring protein and determine if cytokinesis proteins influence each other's dynamics. Project 2. Assembly of cytokinesis proteins in the broad band of precursor nodes: these experiments will clarify the biochemical pathway that assembles the precursor of the contractile ring. We will determine the domains of anillin Mid1p that bind the cortex and downstream proteins and how cytokinesis proteins interact with Mid1p and with each other. Project 3. Transformation of precursor nodes into a contractile ring: this work will provide information required to understand the second step in the assembly of the contractile ring. We will investigate how Cdc12p controls the assembly of actin filaments from nodes, characterize the mechanical process that converts, a broad band of nodes into a contractile ring, characterize how DCS protein Rng3p and phosphorylation affect the structure of Myo2 filaments and determine how cytokinesis proteins are organized in the broad band and the contractile ring. Project 4. Constriction and disassembly of the contractile ring: these experiments will help us understand how cells trigger constriction of the contractile ring and how the ring disassembles as it constricts. We will investigate how the SIN pathway triggers constriction of the contractile ring, explore the factors that limit the rate of constriction of contractile rings and determine how the contractile ring disassembles during constriction.